Lignosulfonic acid (LSA) is a most common cement dispersant. When used in cement compositions LSA reduces the amount of water used, and improves the workability of the cement compositions. However, LSA has the defect of lowering the flowability (slump) of the cement compositions over time.
Furthermore, as the dosage is increased, the calcium salt of LSA causes increases in air entrainment and an overly retarded curing time, in cement compositions.
To cure the defects of the LSA salt the following procedures have been used:
1--Alkali air oxidation of LSA (Japanese Kokai Sho-No. 55-56051); PA0 2--Elimination of the low molecular weight region of LSA by ultrafiltration (GB No. 2092564); PA0 3--Reduction in the low molecular weight region of LSA by ultrafiltration of co-condensates of LSA with naphthalenesulfonic acid and formaldehyde (Japanese Kokai Sho-No. 58-176158); and PA0 4--Converting LSA to a high polymer with hydrogen peroxide, persulfate or the like (Japanese Kokoku Sho-No. 62-103). PA0 (a) Preparing a graft copolymer of acrylic acid with a LSA salt using hydrogen peroxide (U.S. Pat. No. 4,322,301). This copolymer has been used for sludge dispersion stabilizers for excavation of oil fields; and PA0 (b) Preparing a graft copolymer of acrylic acid or methacrylic acid with LSA salt using hydrogen peroxide. These copolymers are used as additives for the aqueous slurry of solid fuels (Japanese Kokai Sho-No. 61-218694). PA0 Calcium lignosulfonate (LSACa); PA0 2-Acrylamide-2-methylpropanesulfonic acid (AS); PA0 Acrylamide (AM); PA0 Acrylic Acid (AA); and PA0 Acrylonitrile (AN). PA0 "%" means "% by weight", and PA0 "part" means "part by weight".
However, these methods have either been economically disadvantageous, or have produced low yields of the product.
Prior art processess for preparing lignosulfonic acid graft copolymers include:
There is however, no application of these copolymers as cement dispersants.